1. Field of the Invention
This invention relates to communication networks. More specifically, the present invention relates to communication over optical networks.
2. Background of the Invention
Various topologies can be used in a network. One such network topology is a ring. Different types of transport technologies can be used on a ring network. One class of these transport technologies relies on multiplexing (e.g., time division multiplexing (TDM), wave division multiplexing (WDM), dense wave division multiplexing (DWDM), etc.).
An optical standard such as Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) in conjunction with a multiplexing scheme is used to deliver various rates of traffic over a single high-speed optical fiber. SONET/SDH is a transmission standard for optical networks that corresponds to the physical layer of the open standards institutes (OSI) network model. One of the protection schemes for SONET/SDH in a ring network involves automatic protection switching (APS) in a bidirectional line switched ring (BLSR) architecture. There are different types of BLSR, including two fiber and four fiber. In addition to BLSR, there is also a uni-directional line switched ring (UPSR) architecture.
Standard BLSR Concatenations
A ring network can be operated by implementing a multiplexing ring transport protocol on a number of network elements that participate as nodes of the ring network. These network elements are connected by spans to form the ring. When using BLSR, each of these spans includes two “sub-spans” on which traffic travels in opposite directions on a number of time slots (referred to herein as channels). The channels in each direction include a set of working channels and a set of protecting channels. Thus, each node has at least two ports, each of which is connect to a different span of the ring. In addition, each of these ports has a receiving side and a transmitting side to which are respectively connected the incoming and outgoing sub-spans.
FIG. 1A illustrates a SONET OC-12 BLSR ring carrying exemplary traffic according to the prior art. In particular, FIG. 1A shows 4 nodes labeled 1–4, where nodes 1 and 3 are each connected to nodes 2 and 4 by different spans to form a ring. FIG. 1A also shows working traffic 110, extra traffic 120, and working traffic 130. The term working traffic is used to refer to traffic carried on a circuit provisioned on the working channels, whereas extra traffic refers to traffic carried on a circuit provisioned on the protecting channels. As is known in the art, extra traffic is preempted during a protection switch.
Since the spans of a BLSR each include two sub-spans which carry traffic in opposite directions, the same direction sub-spans form two “sub-rings” each carrying traffic in the opposite direction.
A circuit is provisioned through the ring 100 by installing cross-connects. For a given circuit, the node within which a cross-connect is installed to add traffic from outside of the ring is referred to as the add node (e.g., for the circuit carrying the working traffic 130 from node 1 to node 3, node 1 would be the add node for that traffic). In contrast, the node within which the cross-connect is installed to drop traffic from the ring is referred to as the drop node (e.g., again, for the circuit carrying the working traffic 130 from node 1 to node 3, node 3 is the drop node). Any node within which a cross-connect is installed that passes traffic from one span to another is referred to as a pass-through node (e.g., for the circuits carrying the working traffic 130, node 4 acts as a pass-through node).
Since the bandwidth requirements for a given circuit may be greater than a single one of the channels, multiple channels can be concatenated together. Thus, each circuit provisioned on a ring has associated therewith a concatenation size. With respect to the example of FIG. 1A, the: 1) working traffic 110 travels on a circuit provisioned on the working channels 1–3, and therefore that circuit has a concatenation size of 3 channels (“3C”); 2) the extra traffic 120 travels on a circuit provisioned on the protecting channels 7–9, and therefore that circuit has a concatenation size of 3C; and 3) the working traffic 130 is carried on a circuit provisioned on the working channel 4, and therefore that circuit has a concatenation size of 1.
In a standard BLSR ring, any use of the working channels configured on a sub-span must be configured on all sub-spans around the ring, and also must be mirrored in the protection channels. For example, if a 3C is configured on a particular set of working channels of any sub-span, then: 1) that 3C must be configured on the same working channels of every one of the sub-spans of the ring; and 2) a corresponding 3C must be preconfigured on the corresponding protection channels of all of the sub-spans of the ring. FIG. 1B illustrates the concatenation configuration for all of the sub-spans of FIG. 1A. In particular, FIG. 1B shows that in an OC-12 ring there are 6 working channels (1–6) and 6 protecting channels (7–12). Each of the protecting channels corresponds to one of the working channels (channel 7 corresponds to channel 1, channel 8 corresponds to channel 2, and so on). The concatenation configuration for a standard BLSR ring identifies the usage of STS and concatenated STS sized components. Thus, FIG. 1B shows the 3C concatenation of the working channels 1–3 (which in FIG. 1A are used between nodes 1 and 2) and its corresponding 3C concatenation mirrored in the protecting channels 7–9 (which in FIG. 1A is used between nodes 4, 3 and 2). In addition, FIG. 1B shows that the working channel 4 is configured as a 1C (which in FIG. 1A is used between nodes 1, 4, and 3).
Thus, the concatenation configuration for a standard BLSR ring is ring based in that it is the same for every sub-span of the ring. To accommodate the concatenation configuration for the ring, the receiving side of the ports of each node connected to spans of ring are programmed with the ring's concatenation configuration. In addition, each node stores a copy of the ring's concatenation configuration so it may reprogram its ports when the system is rebooted or when the line card on which a port resides is replaced. Since the concatenation configuration is the same around the ring and is mirrored in the protecting channels, only a single copy of the concatenation configuration for the working channels of one sub-span needs to be stored in each node.
When there is a failure in a span of the ring, a protection switch is performed. The failure of a span will be recognized by the 2 nodes connected to that span (these nodes are referred to as the switching nodes). These 2 nodes signal the need for a protection switch by transmitting messages. Specifically, each of these nodes transmit messages to each other along the long path (the path that does not include the failed span) and the short path (the path that includes the failed span). The nodes not directly connected to the failed span (referred to as the bridging nodes) will inspect the long path messages as they pass through them. As is well known in the art, responsive to the protection switch, the working traffic on the failed span is switched to the protecting channels of the non-failed spans. The working bandwidth of any span can be switched to the protecting channels of any other span because the same concatenation configuration is configured on the working channels of every span, and that same concatenation configuration is mirrored on the protecting channels. Responsive to the failure being corrected, a protection un-switch is performed as is known in the art.
A disadvantage of the system described in FIGS. 1A–B is that it often does not allow for optimal usage of the ring's bandwidth. For example, while a 3C concatenation between nodes 1 and 2 may be needed, that 3C concatenation may not be optimal for circuit(s) to be provisioned between nodes 1, 4, and 3. More specifically, in the example of FIG. 1A, a circuit with a size of 1C was configured for the working traffic 130. However, this 1C could not use the working channels 1–3 because they must be provisioned as a 3C concatenation to support the circuit carrying the working traffic 110. That is why the circuit carrying the working traffic 130 is provisioned on the working channel 4. While the working traffic 110 and 130 illustrate a limitation with regard to the provisioning of circuits on the working channels, a similar limitation exists with regard to the provisioning of circuits on the protecting channels. In particular, since a circuit with a 3C concatenation was configured between the nodes 1 and 2 for the working traffic 110, there is a mirroring 3C concatenation preconfigured on the corresponding protecting channels 7–9 all the way around the ring (on both sub-rings). However, whether or not a 3C concatenation is required for a particular circuit provisioned on the protecting channels, a 3C concatenation must be used to utilize the protecting channels 7–9.
As more circuits are provisioned on a ring, these concatenation requirements make it harder or impossible to make full use of all of the ring's bandwidth. For example, where a smaller size would suffice, a larger sized concatenation may need to be used because of other circuits provisioned on the ring. Similarly, where a larger sized concatenation would allow for more optimal use, a combination of smaller sets of channels may need to be utilized because of circuits already provisioned on the ring.
Network Element and Ring Network Information Generation and Distribution
In order for a ring network to operate, network element information and ring network information must be generated and stored in each of the nodes of the ring. Various schemes can be used for generating and distributing this information, including a centralized scheme and a distributed scheme.
FIG. 2 illustrates a centralized scheme for generating and distributing the network element and ring network information according to the prior art. In particular, FIG. 2 illustrates a BLSR ring composed of 4 nodes labeled 1–4. The nodes 1–4 in FIG. 2 are oriented in the same manner as the nodes 1–4 in FIG. 1A. In addition, FIG. 2 shows the opposite direction sub-spans of each span of the ring. FIG. 2 also illustrates a network management system 220 in communication with each of the nodes 1–4.
In Block 200 of FIG. 2, the ring illustrated in FIG. 2 is planned. This planning includes the generation of the network element information and ring network information. The network element information includes things such the network elements that will participate as nodes of the ring, the APS node IDs for those nodes, the line cards and ports within each of those network elements that will be connected to spans of the ring, the initial cross-connections to be installed, etc. In contrast, the ring network information includes things such as the ring map, the initial squelch table for each node, etc. From Block 200, control passes to Block 210.
In Block 210, the ring is physically built and the network element and ring network information is entered into the network management system 220. From Block 210, control passes to Block 230. In Block 230, the appropriate network element and ring network information is pushed down to each of the network elements participating in the ring.
One disadvantage to this centralized scheme is that the process of entering the information into the network management system 220 is time consuming and can be subject to human error. Another disadvantage of the centralized scheme is its lack of scalability. For example, each time a circuit is provisioned or unprovisioned from a ring, the squelch tables of each node of that ring must be updated and those updates must be distributed by the network management system 220. Since, it is typical for a given network management system to manage many rings, the network management system can be overwhelmed.
In contrast to the centralized scheme, in a distributed scheme, the nodes of the ring intercommunicate to generate and distribute the ring map and squelch tables. While techniques for distributively generating a ring map and a squelch table for a ring are known, these techniques are not robust in that they do not take into account span failures and how to handle partially built rings.